Estimation of the Impact of Land-Surface Forcing on Temperature Trends in Eastern United States

We are using a method to at least partially identify the impact of land-use changes by computing the difference between the trends of the surface temperature observations (which reflect all the sources of climate forcing, including surface effects) and the NCEPNCAR Reanalysis estimated surface temperatures (with trends only influenced by the assimilated atmospheric temperature trends). This difference would include not only urbanization effects but also changes in agricultural practices, such as irrigation and deforestation, as well as other near surface forcings related to industrialization, such as aerosols. In this work we slightly correct previous results by including the year 1979 within the satellite decades, and by excluding all stations in the West Coast of the US, which were not well correlated with observations. The estimated land-use changes impact on the raw data increases the minimum temperature and decreases the maximum temperature. The impact on the mean temperature has a similar geographical distribution and amplitude to that obtained by Hansen et al (2001) using satellite observations of night-light to discriminate between rural and urban stations. The seasonal cycle results suggest that the impact of the greenhouse gases dominates in the winter, whereas it appears that the impact of surface forcings is more important in the summer. The impact of the adjustment for non-climatic trends in the observations is to increase the trend of the maximum temperature and, to a lesser extent, the minimum temperature, but without affecting the geographical distribution of the trends. Other considerations such as the effect of using a model with constant CO2 in the reanalysis, the use of other reanalyses,